U.S. patent application number 14/111550 was filed with the patent office on 2014-02-06 for diamond sensors, detectors, and quantum devices.
This patent application is currently assigned to Element Six Limited. The applicant listed for this patent is Matthew Lee Markham, Geoffrey Alan Scarsbrook, Daniel James Twitchen. Invention is credited to Matthew Lee Markham, Geoffrey Alan Scarsbrook, Daniel James Twitchen.
Application Number | 20140037932 14/111550 |
Document ID | / |
Family ID | 44243697 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140037932 |
Kind Code |
A1 |
Twitchen; Daniel James ; et
al. |
February 6, 2014 |
DIAMOND SENSORS, DETECTORS, AND QUANTUM DEVICES
Abstract
A synthetic single crystal diamond material comprising: a first
region of synthetic single crystal diamond material comprising a
plurality of electron donor defects; a second region of synthetic
single crystal diamond material comprising a plurality of quantum
spin defects; and a third region of synthetic single crystal
diamond material disposed between the first and second regions such
that the first and second regions are spaced apart by the third
region, wherein the second and third regions of synthetic single
crystal diamond material have a lower concentration of electron
donor defects than the first region of synthetic single crystal
diamond material, and wherein the first and second regions are
spaced apart by a distance in a range 10 nm to 100 .mu.m which is
sufficiently close to allow electrons to be donated from the first
region of synthetic single crystal diamond material to the second
region of synthetic single crystal diamond material thus forming
negatively charged quantum spin defects in the second region of
synthetic single crystal diamond material and positively charged
defects in the first region of synthetic single crystal diamond
material while being sufficiently far apart to reduce other
coupling interactions between the first and second regions which
would otherwise unduly reduce the decoherence time of the plurality
of quantum spin defects and/or produce strain broaden of a spectral
line width of the plurality of quantum spin defects in the second
region of synthetic single crystal diamond material.
Inventors: |
Twitchen; Daniel James;
(Santa Clara, CA) ; Markham; Matthew Lee; (Didcot,
GB) ; Scarsbrook; Geoffrey Alan; (Didcot,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Twitchen; Daniel James
Markham; Matthew Lee
Scarsbrook; Geoffrey Alan |
Santa Clara
Didcot
Didcot |
CA |
US
GB
GB |
|
|
Assignee: |
Element Six Limited
Ballasalla
IM
|
Family ID: |
44243697 |
Appl. No.: |
14/111550 |
Filed: |
May 1, 2012 |
PCT Filed: |
May 1, 2012 |
PCT NO: |
PCT/EP2012/057960 |
371 Date: |
October 21, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61483172 |
May 6, 2011 |
|
|
|
Current U.S.
Class: |
428/220 ;
423/446 |
Current CPC
Class: |
C30B 31/22 20130101;
G06N 10/00 20190101; C30B 29/04 20130101; C30B 25/02 20130101; C30B
33/00 20130101 |
Class at
Publication: |
428/220 ;
423/446 |
International
Class: |
C30B 29/04 20060101
C30B029/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2011 |
GB |
1107552.0 |
Claims
1. A synthetic single crystal diamond material comprising: a first
region of synthetic single crystal diamond material comprising a
plurality of electron donor defects; a second region of synthetic
single crystal diamond material comprising a plurality of quantum
spin defects; and a third region of synthetic single crystal
diamond material disposed between the first and second regions such
that the first and second regions are spaced apart by the third
region, wherein the second and third regions of synthetic single
crystal diamond material have a lower concentration of electron
donor defects than the first region of synthetic single crystal
diamond material, and wherein the first and second regions are
spaced apart by a distance in a range 10 nm to 100 .mu.m which is
sufficiently close to allow electrons to be donated from the first
region of synthetic single crystal diamond material to the second
region of synthetic single crystal diamond material thus forming
negatively charged quantum spin defects in the second region of
synthetic single crystal diamond material and positively charged
defects in the first region of synthetic single crystal diamond
material while being sufficiently far apart to reduce other
coupling interactions between the first and second regions which
would otherwise unduly reduce the decoherence time of the plurality
of quantum spin defects and/or produce strain broaden of a spectral
line width of the plurality of quantum spin defects in the second
region of synthetic single crystal diamond material.
2. A synthetic single crystal diamond material according to claim
1, wherein the third region has a lower concentration of quantum
spin defects than the second region.
3. A synthetic single crystal diamond material according to claim
1, wherein the first, second and third regions are in the form of
layers.
4. A synthetic single crystal diamond material according to claim
1, wherein the first, second and third regions are disposed within
a single layer.
5-13. (canceled)
14. A synthetic single crystal diamond material according to claim
1, wherein the concentration of electron donor defects in the first
region is equal to or greater than: 1.times.10.sup.16
defects/cm.sup.3; 5.times.10.sup.16 defects/cm.sup.3;
1.times.10.sup.17 defects/cm.sup.3; 5.times.10.sup.17
defects/cm.sup.3; 1.times.10.sup.18 defects/cm.sup.3;
5.times.10.sup.18 defects/cm.sup.3; 1.times.10.sup.19
defects/cm.sup.3; or 2.times.10.sup.19 defects/cm.sup.3.
15-16. (canceled)
17. A synthetic single crystal diamond material according to claim
1, wherein the concentration of electron donor defects in the first
region is greater than a concentration of electron donor defects in
the second region by a factor of at least 2, 4, 8, 10, 100, or
1000.
18. A synthetic single crystal diamond material according to claim
1, wherein at least 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the
quantum spin defects in the second region are negatively
charged.
19. (canceled)
20. A synthetic single crystal diamond material according to claim
1, wherein the second region has a thickness equal to or less than:
100 .mu.m; 80 .mu.m; 60 .mu.m; 40 .mu.m; 20 .mu.m; or 10 .mu.m.
21. A synthetic single crystal diamond material according to claim
1, wherein the concentration of quantum spin defects in the second
region is equal to or greater than: 1.times.10.sup.11
defects/cm.sup.3; 1.times.10.sup.12 defects/cm.sup.3;
1.times.10.sup.13 defects/cm.sup.3; 1.times.10.sup.14
defects/cm.sup.3; 1.times.10.sup.15 defects/cm.sup.3;
1.times.10.sup.16 defects/cm.sup.3; 1.times.10.sup.17
defects/cm.sup.3; 1.times.10.sup.18 defects/cm.sup.3.
22. (canceled)
23. A synthetic single crystal diamond material according to claim
1, wherein the concentration of electron donor defects in the
second region including one or more of nitrogen, phosphorous and
silicon, either alone or in combination, is equal to or less than:
1.times.10.sup.17 defects/cm.sup.3; 1.times.10.sup.16
defects/cm.sup.3; 5.times.10.sup.15 defects/cm.sup.3;
1.times.10.sup.15 defects/cm.sup.3; 5.times.10.sup.14
defects/cm.sup.3; 1.times.10.sup.14 defects/cm.sup.3; or
5.times.10.sup.13 defects/cm.sup.3.
24. (canceled)
25. A synthetic single crystal diamond material according to claim
1, wherein the quantum spin defects have a decoherence time T.sub.2
equal to or greater than 0.05 ms, 0.1 ms, 0.3 ms, 0.6 ms, 1 ms, 5
ms, or 15 ms, with corresponding T.sub.2* values equal to or less
than 400 .mu.s, 200 .mu.s, 150 .mu.s, 100 .mu.s, 75 .mu.s, 50
.mu.s, 20 .mu.s, or 1 .mu.s.
26. A synthetic single crystal diamond material according to claim
1, wherein the third region has a thickness equal to or greater
than: 50 nm; 100 nm; 500 nm; 1 .mu.m; 10 .mu.m; or 20 .mu.m.
27. A synthetic single crystal diamond material according to claim
1, wherein the third region has a thickness equal to or less than:
80 .mu.m; 60 .mu.m; 40 .mu.m; or 30 .mu.m.
28. A synthetic single crystal diamond material according to claim
1, wherein the third region has a concentration of electron donor
defects including one or more of nitrogen, phosphorous and silicon,
either alone or in combination, which is equal to or less than:
1.times.10.sup.17 defects/cm.sup.3; 1.times.10.sup.16
defects/cm.sup.3; 5.times.10.sup.15 defects/cm.sup.3;
1.times.10.sup.15 defects/cm.sup.3; 5.times.10.sup.14
defects/cm.sup.3; 1.times.10.sup.14 defects/cm.sup.3; or
5.times.10.sup.13 defects/cm.sup.3.
29. A synthetic single crystal diamond material according to claim
1, wherein the third region has a concentration of quantum spin
defects equal to or less than: 1.times.10.sup.14 defects/cm.sup.3;
1.times.10.sup.13 defects/cm.sup.3; 1.times.10.sup.12
defects/cm.sup.3; 1.times.10.sup.11 defects/cm.sup.3; or
1.times.10.sup.10 defects/cm.sup.3.
30-43. (canceled)
Description
FIELD OF INVENTION
[0001] The present invention relates to synthetic chemical vapour
deposited (CVD) diamond material for use in sensing, detecting and
quantum processing applications.
BACKGROUND OF INVENTION
[0002] Point defects in synthetic diamond material, particularly
quantum spin defects and/or optically active defects, have been
proposed for use in various sensing, detecting, and quantum
processing applications including: magnetometers; spin resonance
devices such as nuclear magnetic resonance (NMR) and electron spin
resonance (ESR) devices; spin resonance imaging devices for
magnetic resonance imaging (MRI); and quantum information
processing devices such as for quantum computing.
[0003] Many point defects have been studied in synthetic diamond
material including: silicon containing defects such as
silicon-vacancy defects (Si-V), silicon di-vacancy defects
(Si-V.sub.2), silicon-vacancy-hydrogen defects (Si-V:H), silicon
di-vacancy hydrogen defects (S-V.sub.2:H); nickel containing
defect; chromium containing defects; and nitrogen containing
defects such as nitrogen-vacancy defects (N-V), di-nitrogen vacancy
defects (N-V-N), and nitrogen-vacancy-hydrogen defects (N-V-H).
These defects are typically found in a neutral charge state or in a
negative charge state. It will be noted that these point defects
extend over more than one crystal lattice point. The term point
defect as used herein is intended to encompass such defects but not
include larger cluster defects, such as those extending over ten or
more lattice points, or extended defects such as dislocations which
may extend over many lattice points.
[0004] It has been found that certain defects are particularly
useful for sensing, detecting, and quantum processing applications
when in their negative charge state. For example, the negatively
charged nitrogen-vacancy defect (NV.sup.-) in synthetic diamond
material has attracted a lot of interest as a useful quantum spin
defect because it has several desirable features including: [0005]
(i) Its electron spin states can be coherently manipulated with
high fidelity owing to an extremely long coherence time (which may
be quantified and compared using the transverse relaxation time
T.sub.2 and/or T.sub.2*); [0006] (ii) Its electronic structure
allows the defect to be optically pumped into its electronic ground
state allowing such defects to be placed into a specific electronic
spin state even at non-cryogenic temperatures. This can negate the
requirement for expensive and bulky cryogenic cooling apparatus for
certain applications where miniaturization is desired. Furthermore,
the defect can function as a source of photons which all have the
same spin state; and [0007] (iii) Its electronic structure
comprises emissive and non-emissive electron spin states which
allows the electron spin state of the defect to be read out through
photons. This is convenient for reading out information from
synthetic diamond material used in sensing applications such as
magnetometry, spin resonance spectroscopy and imaging. Furthermore,
it is a key ingredient towards using the NV.sup.- defects as qubits
for long-distance quantum communications and scalable quantum
computation. Such results make the NV.sup.- defect a competitive
candidate for solid-state quantum information processing (QIP).
[0008] The NV.sup.- defect in diamond consists of a substitutional
nitrogen atom adjacent to a carbon vacancy as shown in FIG. 1a. Its
two unpaired electrons form a spin triplet in the electronic ground
state (.sup.3A), the degenerate m.sub.s=.+-.1 sublevels being
separated from the m.sub.s=0 level by 2.87 GHz. The electronic
structure of the NV.sup.- defect is illustrated in FIG. 1b from
Steingert et al. "High sensitivity magnetic imaging using an array
of spins in diamond", Review of Scientific Instruments 81, 043705
(2010). The m.sub.s=0 sublevel exhibits a high fluorescence rate
when optically pumped. In contrast, when the defect is excited in
the m.sub.s=.+-.1 levels, it exhibits a higher probability to cross
over to the non-radiative singlet state (.sup.1A) followed by a
subsequent relaxation into m.sub.s=0. As a result, the spin state
can be optically read out, the m.sub.s=0 state being "bright" and
the m.sub.s=.+-.1 states being dark. When an external magnetic
field is applied, the degeneracy of the spin sublevels
m.sub.s=.+-.1 is broken via Zeeman splitting. This causes the
resonance lines to split depending on the applied magnetic field
magnitude and its direction. This dependency can be used for vector
magnetometry as the resonant spin transitions can be probed by
sweeping the microwave (MW) frequency resulting in characteristic
dips in the optically detected magnetic resonance (ODMR) spectrum
as shown in FIG. 2a from Steinert et al.
[0009] Steinert et al. employed ion implantation to create a
homogenous layer of negatively charged NV.sup.- centres into an
ultrapure {100} type IIa diamond. The ensemble NV.sup.- sensor was
found to offer a higher magnetic sensitivity due to the amplified
fluorescence signal from a plurality of sensing spins. Another
option is vector reconstruction since the diamond lattice imposes
four distinct tetrahedral NV.sup.- orientations as shown in FIG. 2b
from Steinert et al. The magnetic field projections along each of
these axes can be measured as a single composite spectrum and a
numerical algorithm used to reconstruct the full magnetic field
vector. The magnitude (B) and orientation (.theta..sub.B,
.phi..sub.B) of the external magnetic field can be calculated by
analyzing the ODMR spectra based on an unconstrained least-square
algorithm.
[0010] One major problem in producing materials suitable for
quantum applications is preventing quantum spin defects from
decohering, or at least lengthening the time a system takes to
decohere (i.e. lengthening the "decoherence time"). A long
decoherence time is desirable in applications such as quantum
computing as it allows more time for the operation of an array of
quantum gates and thus allows more complex quantum computations to
be performed. A long decoherence time is also desirable for
increasing sensitivity to changes in the electric and magnetic
environment in sensing applications.
[0011] WO 2010010344 discloses that single crystal synthetic CVD
diamond material which has a high chemical purity, i.e. a low
nitrogen content, and wherein a surface of the diamond material has
been processed to minimise the presence of crystal defects, can be
used to form a solid state system comprising a quantum spin defect.
Where such materials are used as a host for quantum spin defects,
long decoherence times are obtained at room temperature and the
frequency of the optical transitions used to read/write to devices
are stable.
[0012] WO 2010010352 discloses that by carefully controlling the
conditions under which single crystal synthetic CVD diamond
material is prepared, it is possible to provide synthetic diamond
material which combines a very high chemical purity with a very
high isotopic purity. By controlling both the chemical purity and
the isotopic purity of the materials used in the CVD process, it is
possible to obtain synthetic diamond material which is particularly
suitable for use as a host for a quantum spin defect. Where such
materials are used as a host for quantum spin defects, long
decoherence times are obtained at room temperature and the
frequency of the optical transitions used to read/write to the
devices are stable. A layer of synthetic diamond material is
disclosed which has a low nitrogen concentration and a low
concentration of .sup.13C. The layer of synthetic diamond material
has very low impurity levels and very low associated point defect
levels. In addition, the layer of synthetic diamond material has a
low dislocation density, low strain, and vacancy and
self-interstitial concentrations which are sufficiently close to
thermodynamic values associated with the growth temperature that
its optical absorption is essentially that of a perfect diamond
lattice.
[0013] In light of the above, it is evident that WO 2010010344 and
WO 2010010352 disclose methods of manufacturing high quality
"quantum grade" single crystal synthetic CVD diamond material. The
term "quantum grade" is used herein for diamond material which is
suitable for use in applications that utilize the material's
quantum spin properties. Specifically, the quantum grade diamond
material's high purity makes it possible to isolate single defect
centres using optical techniques known to the person skilled in the
art. The term "quantum diamond material" is also used to refer to
such material.
[0014] One problem with quantum materials is that single photon
emission from quantum spin defects in such materials can be very
weak. For example, NV.sup.- defects in diamond exhibit a broad
spectral emission associated with a Debye-Waller factor of the
order of 0.05, even at low temperature. Emission of single photons
in the Zero-Phonon Line (ZPL) is then extremely weak, typically of
the order of a few thousands of photons per second. Such counting
rates might be insufficient for the realization of advanced QIP
protocols based on coupling between spin states and optical
transitions within reasonable data acquisition times.
[0015] The problem of weak emission may be alleviated to some
extent by increasing the number of quantum spin defects such that a
large number of emitting species exists in the material. To form
negatively charged defects requires an electron donor such as a
nitrogen or phosphorous. Accordingly, to increase the number of
negatively charged defects one could increase the concentration of
electron donors within the material. However, such electron donors
may undergo dipole coupling with the negatively charged quantum
spin defects lowering the decoherence time of the negatively charge
quantum spin defects. Accordingly, the problem to be solved becomes
how to increase the number of negatively charged quantum spin
defects while not unduly lowering the decoherence time of the
negatively charged quantum spin defects. Alternatively, for certain
applications it may be desirable to have relatively few negatively
charged quantum spin defects but where each negatively charged
quantum spin defect has a very high decoherence time. The problem
then is how to form a negatively charged quantum spin defect while
ensuring that the electron donor required to form the defect does
not unduly lower the decoherence time.
[0016] It is an aim of certain embodiments of the present invention
to at least partially solve one or more of the aforementioned
problems.
SUMMARY OF INVENTION
[0017] The present inventors have realized that the length scale
over which charge transfer occurs is different to that over which
processes that lead to decoherence occur (e.g. dipole spin
coupling). As such, in principle it is possible to locate an
electron donor sufficiently close to a quantum spin defect for
charge transfer to occur in order to form a negatively charged
quantum spin defect but sufficiently far to minimize strain and
dipole coupling which would otherwise lead to a reduction in the
decoherence time of the quantum spin defect or spectral line width
broadening of the quantum spin defect. Furthermore, the present
inventors have realized that such an arrangement can be achieved in
practice by locating electron donor defects in a first region of
material, locating quantum spin defects in a second region of
material spaced apart from the first region of material comprising
the electron donor defects, and forming the regions such that they
are sufficiently closely spaced that charge transfer can occur from
the first region to the second region to enable formation of
negatively charged quantum spin defects in the second region yet
sufficiently far apart that the electron charge donor defects do
not undergo substantial dipole coupling with the quantum spin
defects to unduly reduce the decoherence time of the quantum spin
defects and/or produce strain broaden of the spectral line width of
the quantum spin defects.
[0018] In light of the above, a first aspect of the present
invention provides a synthetic single crystal diamond material
comprising: [0019] a first region of synthetic single crystal
diamond material comprising a plurality of electron donor defects;
[0020] a second region of synthetic single crystal diamond material
comprising a plurality of quantum spin defects; and [0021] a third
region of synthetic single crystal diamond material disposed
between the first and second regions such that the first and second
regions are spaced apart by the third region, [0022] wherein the
second and third regions of synthetic single crystal diamond
material have a lower concentration of electron donor defects than
the first region of synthetic single crystal diamond material, and
[0023] wherein the first and second regions are spaced apart by a
distance in a range 10 nm to 100 .mu.m which is sufficiently close
to allow electrons to be donated from the first region of synthetic
single crystal diamond material to the second region of synthetic
single crystal diamond material thus forming negatively charged
quantum spin defects in the second region of synthetic single
crystal diamond material and positively charged defects in the
first region of synthetic single crystal diamond material while
being sufficiently far apart to reduce other coupling interactions
between the first and second regions which would otherwise unduly
reduce the decoherence time of the plurality of quantum spin
defects and/or produce strain broaden of a spectral line width of
the plurality of quantum spin defects in the second region of
synthetic single crystal diamond material.
[0024] The above definition takes into account the fact that it is
impossible to form a perfect single crystal diamond lattice
structure. As such, there will inevitable be some defects present
in every region of the material, some of which may form quantum
spin defects and some of which may form electron donor defects. The
important point here is to note that the method of fabricating each
of the different regions can be tuned to favour formation of one
type of defect over another type of defect or tuned to minimize a
range of defect types. As such, the first region can be fabricating
using a method suitable to increase the number of electron donor
defects and the second region can be fabricated using a method
suitable for introducing quantum spin defects into the region while
ensuring that a relatively low number of electron donor defects are
introduced into the second region when compared to the first region
of material. Furthermore, these different regions can be fabricated
with a third spacer region therebetween such that the first and
second regions are a specific distance apart to meet the functional
requirements as described above.
[0025] The third intermediate region of material disposed between
the first and second regions can be fabricated by a method suitable
for forming relatively high purity diamond material which has few
electron donor defects relative to the first region. The third
region may also comprise few quantum spin defects relative to the
second region. The third intermediate region may form definitive
boundary interfaces with both the first and second regions. For
example, in one arrangement a layer structure comprising at least
an electron donor layer (first region), a quantum spin defect
acceptor layer (second region), and an intermediate spacer layer
(third region) may be provided. However, it is also envisaged that
the donor and acceptor regions do not need to be layers and do not
need to be separated by an intermediate layer. One alternative
example is to form donor and acceptor regions, for example using
implantation methods, which are laterally separated rather than
vertically separated into layers. Another alternative example is a
vertically stacked layer structure comprising an electron donor
layer and a quantum spin defect acceptor layer but no intermediate
layer. In this arrangement, the donor layer may have a
concentration of electron donors which is ramped downwards towards
the acceptor layer. As such, there may be no separate and readily
discernable intermediate layer although there will be an
identifiable intermediate region having a relatively low
concentration of electron donors. In effect the electron donor
layer is graduated to have different regions including a region
having a relatively high concentration of electron donors and a
region having a relatively low concentration of electron donors
adjacent the quantum spin defect region.
[0026] Yet another possibility is that the third region is formed
to have the same or a similar composition to the second region of
material, the regions being differentiated by controlled optical
address in use rather then chemical and/or crystallographic
composition. For example, a synthetic single crystal diamond
material may be formed with a first electron donor layer (first
region) and a second quantum spin defect layer (second and third
region). In use, a region of the second quantum spin defect layer
spaced apart from the first layer by a distance in a range 10 nm to
100 .mu.m may be optically addressed, quantum spin defects in this
region being sufficiently close to the electron donor layer to
receive electrons while being sufficiently far from the electron
donor layer to reduce other coupling interactions with the electron
donor layer which would otherwise unduly reduce the decoherence
time of the plurality of quantum spin defects and/or produce strain
broaden of a spectral line width of the plurality of quantum spin
defects in the second region of synthetic single crystal diamond
material. In this arrangement, the intermediate region between the
electron donor layer and the region of optically addressed quantum
spin defects is formed by a portion of the second layer adjacent
the electron donor layer.
[0027] Another alternative would be to form a synthetic single
crystal diamond material comprising a single layer of quantum spin
defects and implant electron donors into laterally spaced regions
of the layer. Such a layer would then contain electron donor
regions and quantum spin defect regions in a similar manner to the
previously described two layer system, the quantum spin defect
regions forming both the second and third regions of the invention.
As with the previously described arrangement, the second and third
regions may be differentiated by controlled optical address such
that portions of the quantum spin defect regions which are spaced
apart from the electron donor regions are optically addressed.
[0028] According to a second aspect of the present invention there
is provided a method of manufacturing a synthetic single crystal
diamond material as described above. The firs, second and third
regions are preferably formed using a CVD technique, optionally
including implantation techniques to form one or more of the
regions. However, according to one possible embodiment the first
region containing the electron donor defects may be formed by the
substrate such that the substrate forms an integral component of
the layered structure. Examples of suitable synthesis methods are
discussed in the detailed description.
[0029] According to a third aspect of the present invention there
is provided a synthetic diamond device component for use in a
sensing, detecting or quantum spin device, said device component
formed of a synthetic single crystal diamond material as described
above.
[0030] According to a fourth aspect of the present invention there
is provided a device comprising a device component as described
above. The device may comprise a light source for optically pumping
one or more of the plurality of quantum spin defects in the second
region of single crystal synthetic diamond material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] For a better understanding of the present invention and to
show how the same may be carried into effect, embodiments of the
present invention will now be described by way of example only with
reference to the accompanying drawings, in which:
[0032] FIG. 1a illustrates the atomic structure of an NV.sup.-
defect;
[0033] FIG. 1b illustrates the electronic structure of an NV.sup.-
defect;
[0034] FIG. 2a illustrates a characteristic fluorescence spectrum
obtained from a plurality of NV.sup.- defects manipulated by a
varying microwave frequency;
[0035] FIG. 2b illustrates the orientation of four crystallographic
NV.sup.- axes in a diamond crystal;
[0036] FIGS. 3(a) to 3(g) illustrate synthetic single crystal
diamond materials according to embodiments of the present
invention;
[0037] FIG. 4 illustrates a method of making a layered synthetic
single crystal diamond material according to an embodiment of the
present invention;
[0038] FIG. 5 shows a schematic diagram of a spin resonance device
according to an embodiment of the present invention;
[0039] FIG. 6 shows a schematic diagram of a spin resonance device
according to another embodiment of the present invention;
[0040] FIG. 7 shows a schematic diagram of a spin resonance device
according to another embodiment of the present invention;
[0041] FIG. 8 shows a schematic diagram of a spin resonance device
according to another embodiment of the present invention;
[0042] FIG. 9 shows a schematic diagram of a spin resonance device
according to another embodiment of the present invention;
[0043] FIG. 10 shows a schematic diagram of a microfluidic cell
comprising a layered synthetic single crystal diamond material for
use in a diamond quantum device according to an embodiment of the
present invention; and
[0044] FIG. 11 shows a schematic diagram of a spin resonance device
for use with a microfluidic cell such as that illustrated in FIG.
10.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0045] FIGS. 3(a) to 3(c) illustrate layered synthetic single
crystal diamond materials according to embodiments of the present
invention.
[0046] FIG. 3(a) shows a layered synthetic single crystal diamond
material comprising a three layer structure. This layered structure
may be entirely formed in a single crystal of synthetic diamond
material such that the layers share a common crystal lattice. A
first layer 2 comprises a plurality of electron donor defects. A
second layer 4 comprises a plurality of quantum spin defects. A
third layer 6 is disposed between the first and second layers 2, 4
such that the first and second layers 2, 4 are spaced apart by a
distance in a range 10 nm to 100 .mu.m. This distance is selected
to allow electrons to be donated from the first layer 2 to the
second layer 4 thus forming negatively charged quantum spin defects
in the second layer 4. Furthermore, the distance between the first
and second layers 2, 4 is selected to ensure dipole coupling
between electron donor defects in the first layer 2 and quantum
spin defects in the second layer 4 is low. This ensures that the
decoherence time of the quantum spin defects in the second layer 4
is high and that strain broadening of the spectral line emission
from the quantum spin defects in the second layer 4 is low. The
second layer 4 has a lower concentration of electron donor defects
than the first layer 2. This ensures that decoherence reduction and
spectral line broadening of the quantum spin defects due to
electron donor defects in the second layer 4 is relatively low.
Furthermore, the third layer 6 has a lower concentration of
electron donor defects than the first layer 2 and a lower
concentration of quantum spin defects than the second layer 4.
Again, this ensures that decoherence reduction and spectral line
broadening of the quantum spin defects in the second layer 4 due to
defects in the third layer 6 is relatively low.
[0047] FIG. 3(b) shows a variant of the layered structure
illustrated in FIG. 3(a). This layered structure comprises the same
three layers 2, 4, 6 as described above. In addition, the layered
structure comprises a bottom layer 8 and a top layer 10
encapsulating the three layer structure. The bottom layer 8 and the
top layer 10 may, for example, comprise high purity diamond
material of a similar nature to that provided in layer 6.
[0048] FIG. 3(c) shows yet another variant of the layered structure
illustrated in FIG. 3(a). The layered structure comprises layers 2,
4, 6, 8, 20 as described in relation to FIG. 3(b). In addition, a
further layer of boron doped single crystal diamond material 12 is
provided to form an electrically semi-conductive or fully metallic
conductive layer. Charge can be passed through this additional
layer and can be used to electrically control the state of the
quantum spin defects in the layer 4. Alternatively, different
surface terminations can be utilized to provide electrical control
of the state of the quantum spin defects. The electron spatial
distribution within the diamond material can thus be controlled by
applying energy to the material, for example, by way of an electric
field to cause electrons to be donated from the electron donor
defects to the quantum spin defect.
[0049] Other variants are also envisaged. For example, the electron
donor defects may be provided in a diamond substrate on which the
layered structure is grown such that the substrate forms an
integral portion of the final layered structure. One or more of the
layers may be formed to have reduced levels of .sup.13C to further
increase decoherence time as .sup.13C is a spin active nucleus
which can detrimentally couple with the quantum spin defects.
Levels of other defects may also be kept low. Additional functional
layers may also be provided such as further layers of quantum spin
defects or further electrically conductive layers to form
electronic components.
[0050] FIG. 3(d) shows another variant of the layered structure
illustrated in FIG. 3(a). A first layer 2 comprises a plurality of
electron donor defects. A second layer 4 comprises a plurality of
quantum spin defects. The electron donor layer 2 has a
concentration of electron donors which is ramped downwards towards
the quantum spin defect layer 4 such that a region 14 of the
electron donor layer 2 adjacent the quantum spin defect layer 4 has
a relatively low concentration of electron donors. As such, in many
respects this structure is similar to the structure shown in FIG.
3(a) with region 14 in FIG. 3(d) being functionally equivalent to
layer 6 in FIG. 3(a). The difference here is that intermediate
region 14 is arguably not separate layer as in FIG. 3(a).
[0051] FIG. 3(e) shows another variant in which one or more
electron donor regions 2, quantum spin defect regions 4, and
intermediate regions 6 are formed in a single layer. In this
arrangement, the electron donor regions 2 and quantum spin defect
regions 4 are laterally separated rather than vertically separated
into layers. The different regions may be formed by using
implantation methods. For example, electron donor species may be
implanted into regions 2 and quantum spin defects may be implanted
into regions 4.
[0052] FIG. 3(f) shows a variant of the arrangement shown in FIG.
3(e) in which the layer of single crystal diamond material
comprises one or more electron donor regions 2 and one or more
quantum spin defect regions 4. No chemically discernable
intermediate regions are provided. Rather, in use a portion 16 of a
quantum spin defect region which is spaced apart from an electron
donor region by a distance in a range 10 nm to 100 .mu.m is
optically addressed, quantum spin defects in this region being
sufficiently close to the electron donor region to receive
electrons while being sufficiently far from the electron donor
region to reduce other coupling interactions with the electron
donor layer which would otherwise unduly reduce the decoherence
time of the plurality of quantum spin defects and/or produce strain
broaden of a spectral line width of the plurality of quantum spin
defects in the second region of synthetic single crystal diamond
material. In this arrangement, intermediate regions 6 between the
electron donor regions 2 and the regions of optically addressed
quantum spin defects 16 are defined by controlled optical
addressing. The structured layer can be formed by implanting
electron donor species into a layer comprising quantum spin
defects.
[0053] FIG. 3(g) shows another variant of the arrangement shown in
FIG. 3(f) in which the layer of single crystal diamond material
comprises one or more electron donor regions 2 and one or more
quantum spin defect regions 4. In this arrangement the
concentration of electron donors in the electron donor regions is
variable. In particular, in the illustrated arrangement the
concentration of electron donors in the electron donor regions is
decreased in portions adjacent to the quantum spin defect regions
to form relatively low electron donor regions 18 which function as
intermediate spacer regions.
[0054] FIG. 4 shows a method of making a layered synthetic single
crystal diamond material as illustrated in FIG. 3(a). The method
starts with a substrate 20 on which the layered structure is to be
deposited. In Step A, a first layer 22 may be formed by growing a
layer of CVD diamond material in an atmosphere containing nitrogen
such that electron donating nitrogen defects are incorporated into
the layer. In Step B, a further layer 24 (the third layer in the
previous definition) can subsequently be grown thereon by reducing
the nitrogen concentration in the process gas such that a high
purity layer is formed. In Step C, a top layer 26 of nitrogen
containing single crystal diamond material can be grown by
increasing the nitrogen concentration in the process gas.
Subsequently, in Step D the three layer structure 22, 24, 26 is
removed from the substrate. In Step E the top layer can be
irradiated to form vacancy defects within the layer and annealed to
allow the vacancy defects to migrate to, and pair with, nitrogen
defects to form a layer 28 containing nitrogen-vacancy (NV)
defects. Electron donation can then occur from the nitrogen defects
in the bottom layer to the NV defects in the top layer thus forming
NV.sup.- defects in the top layer 28 which may be used for sensing,
detecting and quantum processing applications. Because the electron
donating nitrogen species in the bottom layer 22 (which will now be
positively charged having donated an electron to an NV defect) are
spaced apart from the NV.sup.- defects in the top layer 28, then
the magnitude of dipole coupling between the NV.sup.- defects and
the nitrogen defects is reduced and the decoherence time of the
NV.sup.- defects can thus be increased and/or strain broaden of the
spectral line width of the NV.sup.- defects can be reduced.
[0055] Alternatives to the aforementioned method are envisaged. For
example, the electron donor defects are not required to be nitrogen
defects and could instead be phosphorous defects, silicon defects
or any other electron donating diamond defect.
[0056] Defects may be implanted into diamond material to form one
or more of the layers rather than being grown into the material
during diamond synthesis. For example, techniques are known for
implanting impurity atoms such as nitrogen, phosphorous, and
silicon into diamond material. As such, in an alternative to the
previously described example, the top layer 26 may be grown with a
low nitrogen process gas in a similar manner to the intermediate
layer 24 and then impurity atoms such as nitrogen atoms implanted
into the top layer 26 to form the quantum spin defects after
irradiation and/or annealing steps.
[0057] Impurity-vacancy quantum spin defects may be formed by
irradiation and/or annealing. Irradiation can be used to form
vacancies which on heating/annealing can migrate through the
diamond material until they are captured by impurity defects such
as isolated nitrogen point defects to form impurity-vacancy quantum
spin defects. The annealing may be performed during or after
irradiation. The annealing may involve heating the diamond material
to a temperature equal to or grater than 600.degree. C.,
700.degree. C., 800.degree. C., 900.degree. C., 1000.degree. C., or
1200.degree. C. In addition, or as an alternative, to the annealing
forming impurity-vacancy quantum spin defects, annealing can also
aid in removing crystallographic defects, e.g. damage formed by
implanting impurity atoms. Annealing may be performed in one or
more step. For example, the anneal may be performed step-wise at
different temperatures, e.g. a first anneal at a first temperature
and a second anneal at a second temperature which is different from
the first temperature (higher or lower). One advantageous anneal is
at a temperature which is sufficiently high to repair
crystallographic defects/damage but sufficiently low such that
impurity-vacancy defects are not broken up. For example, a first
anneal may be performed at a temperature sufficient to promote
formation of impurity-vacancy quantum spin defects and then a
second anneal may be performed at a higher temperature which
repairs crystallographic defects/damage while not being so high as
to break up the impurity-vacancy defects.
[0058] If sufficient vacancies are present in the as-grown material
then no irradiation step may be required to form vacancies. In such
a situation, the vacancies present in the as-grown material can be
annealed to migrate through the material and be captured by
impurity defects to form impurity-vacancy quantum spin defects.
Furthermore, it is also possible under certain growth conditions to
incorporate impurity-vacancy quantum spin defects directly into the
diamond material as a unit during growth. In such a situation,
neither irradiation not annealing may be required. In this
alternative, impurity-vacancy quantum spin defects are formed
during growth of the diamond material rather than using post-growth
treatments such as irradiation and annealing.
[0059] While the aforementioned embodiment describes the formation
of NV.sup.- defects as the quantum spin defects, other defects may
be used. Various point defects are known in diamond material
including silicon containing defects, nickel containing defects,
chromium containing defects, and nitrogen containing defects. While
it is envisaged that preferred embodiments will utilize nitrogen
containing NV.sup.- defects because of the advantageous properties
of this defect as described in the background section, it is also
envisaged than certain embodiments of this invention may be
applicable to other types of negatively charged defects which are
suitable for sensing, detecting and quantum processing
applications.
[0060] The electron donor layer may have a thickness equal to or
greater than: 10 nm; 100 nm; 5 .mu.m; 50 .mu.m; 100 .mu.m; or 500
.mu.m. The electron donor layer may be formed from a synthetic CVD
(chemical vapour deposited) or synthetic HPHT (high pressure high
temperature) diamond material. Electron donor defects may be formed
in the material during growth or by post-growth implantation. The
upper limit to the thickness of the electron donor layer is not
critical to the functioning of the invention. If the electron donor
layer also functions as a supporting substrate for the layered
structure it may be relatively thick. However, as thick layers of
single crystal diamond material are more difficult and expensive to
form, the electron donor layer will usually be less than 2 mm thick
and will more usually be less than 1 mm thick.
[0061] The electron donor layer should have a relatively high
concentration of electron donor defects such as nitrogen,
phosphorous and/or silicon. For example, the concentration of
electron donor defects may be equal to or greater than:
1.times.10.sup.16 defects/cm.sup.3; 5.times.10.sup.16
defects/cm.sup.3; 1.times.10.sup.17 defects/cm.sup.3;
5.times.10.sup.17 defects/cm.sup.3; 1.times.10.sup.18
defects/cm.sup.3; 5.times.10.sup.18 defects/cm.sup.3;
1.times.10.sup.19 defects/cm.sup.3; or 2.times.10.sup.19
defects/cm.sup.3. In practice it is difficult to incorporate much
higher concentrations and the layer will generally have a
concentration of electron donor defects equal to or less than
10.sup.22 defects/cm.sup.3, 10.sup.21 defects/cm.sup.3, or
10.sup.20 defects/cm.sup.3.
[0062] In order to ensure that there is sufficient electron
donation from the electron donor layer to the quantum spin defect
layer, in some applications it is useful to ensure that there is a
greater concentration of electron donors in the electron donor
layer than the concentration of quantum spin defects in the quantum
spin defect layer. This is because the efficiency of electron
donation between the electron donors and the quantum spin defects
will generally not be 100%. As such, providing an excess of
electron donors ensures that a significant portion of the quantum
spin defects will receive an electron. According to certain
arrangements the concentration of electron donors in the electron
donor layer/region is greater than the concentration of quantum
spin defects in the quantum spin defect layer/region by a factor of
at least 2, 4, 8, 10, 100, or 1000. Furthermore, according to
certain arrangements the concentration of electron donor defects in
the electron donor layer/region is greater than a concentration of
electron donor defects in the quantum spin defect layer/region by a
factor of at least 2, 4, 8, 10, 100, or 1000. Advantageously, at
least 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the quantum spin
defects will receive an electron to form a negatively charged
quantum spin defect.
[0063] The quantum spin defect layer may have a thickness equal to
or greater than: 1 nm; 5 nm; 10 nm; 50 nm; 100 nm; 500 nm; or 1
.mu.m. Furthermore, the quantum spin defect layer may have a
thickness equal to or less than: 100 .mu.m; 80 .mu.m; 60 .mu.m; 40
.mu.m; 20 .mu.m; or 10 .mu.m. Ranges comprising combinations of
these lower and upper boundaries for the thickness of the quantum
spin defect layer are envisaged. The specific layer thickness will
depend to some extent on the device application and the
concentration of quantum spin defects within the layer. For
example, if a reasonably high concentration of quantum spin defects
are present in the quantum spin layer then making the layer very
thin can enable individual quantum spin defects to be optically
isolated. Of course, if the layer becomes too thick then a portion
of the layer which is farthest from the electron donor layer will
be too far from the electron donor layer to receive electrons
therefrom to form negatively charged quantum spin defects. As such,
the layer thickness and concentration of quantum spin defects may
be controlled such that there is a sufficient number of quantum
spin defects for a particular application and the quantum spin
defects are sufficiently close to the electron donor layer such
that electron donation can occur in order to form negatively
charged quantum spin defects. Usually, this will entail the quantum
spin defect layer being very thin and relatively close to the
electron donor layer but not so close that extensive dipole
coupling occurs between the electron donor layer and the quantum
spin defect layer.
[0064] The quantum spin defect layer is preferably formed of
synthetic single crystal CVD diamond material. Quantum spin defects
may be formed in the material during growth or by post-growth
implantation. The quantum spin defects may comprise one or more of:
a negatively charged silicon containing defect; a negatively
charged nickel containing defect; a negatively charged chromium
containing defect; and a negatively charged nitrogen containing
defect. For many applications, the negatively charged
nitrogen-vacancy defect (NV.sup.-) is advantageous because of the
useful properties of this defect as discussed in the background
section.
[0065] The concentration of quantum spin defects will to some
extent depend on the desired application. In applications which
require individual quantum spin defects to be optically isolated
and addressable then the concentration of quantum spin defects is
advantageously sufficiently low such that individual quantum spin
defects can be more easily individually addressed. Alternatively,
in applications where a plurality of quantum spin defects are used
to sense a change in the environment as a group without requiring
individual quantum spin defects to be isolated and separately
addressable then a higher concentration of quantum spin defects can
be provided. For example, the concentration of quantum spin defects
may be equal to or greater than: 1.times.10.sup.11
defects/cm.sup.3; 1.times.10.sup.12 defects/cm.sup.3;
1.times.10.sup.13 defects/cm.sup.3; 1.times.10.sup.14
defects/cm.sup.3; 1.times.10.sup.15 defects/cm.sup.3;
1.times.10.sup.16 defects/cm.sup.3; 1.times.10.sup.17
defects/cm.sup.3; 1.times.10.sup.18 defects/cm.sup.3. Furthermore,
the concentration of quantum spin defects may be equal to or less
than: 4.times.10.sup.18 defects/cm.sup.3; 2.times.10.sup.18
defects/cm.sup.3; 1.times.10.sup.18 defects/cm.sup.3;
1.times.10.sup.17 defects/cm.sup.3; or 1.times.10.sup.16
defects/cm.sup.3. Ranges comprising combinations of these lower and
upper boundaries for the thickness of the quantum spin defect layer
are envisaged. For example, the concentration of quantum spin
defects may in a range: 1.times.10.sup.11 defects/cm.sup.3 to
4.times.10.sup.18 defects/cm.sup.3; 1.times.10.sup.12
defects/cm.sup.3 to 1.times.10.sup.17 defects/cm.sup.3; or
1.times.10.sup.13 defects/cm.sup.3 to 1.times.10.sup.16
defects/cm.sup.3. For higher concentration applications the
concentration of quantum spin defects may in a range
1.times.10.sup.15 defects/cm.sup.3 to 4.times.10.sup.18
defects/cm.sup.3; 1.times.10.sup.16 defects/cm.sup.3 to
2.times.10.sup.18 defects/cm.sup.3; or 1.times.10.sup.17
defects/cm.sup.3 to 1.times.10.sup.18 defects/cm.sup.3. According
to one configuration the number of electron donating defects formed
in the electron donor layer is larger than the number of quantum
spin defects formed in the quantum spin defect layer. A low
concentration of quantum spin defects aids in ensuring that the
quantum spin defects have a high decoherence time, narrow spectral
line width, and that the quantum spin defects can be optically
isolated. A higher number of electron donating defects in the
electron donor layer will ensure that there is a high likelihood of
charge transfer to form a negatively charged quantum spin
defect.
[0066] The concentration of other defects within the quantum spin
defect layer should be low to avoid interactions which lead to a
decrease in the decoherence time or increase absorbance. For
example, for example, the concentration of electron donor defects
such a one or more of nitrogen, phosphorous and silicon, either
alone or in combination, can be equal to or less than:
1.times.10.sup.17 defects/cm.sup.3; 1.times.10.sup.16
defects/cm.sup.3; 5.times.10.sup.15 defects/cm.sup.3;
1.times.10.sup.15 defects/cm.sup.3; 5.times.10.sup.14
defects/cm.sup.3; 1.times.10.sup.14 defects/cm.sup.3; or
5.times.10.sup.13 defects/cm.sup.3. In many applications it is
desirable to have the concentration of other defects as low as
possible in the quantum spin defect layer. However, in practice it
is usual that other defects will be present at a concentration of
at least 1.times.10.sup.10 defects/cm.sup.3.
[0067] For certain applications the quantum spin defect layer may
have one or more of: a neutral single substitutional nitrogen
concentration equal to or less than 20 ppb, 10 ppb, 5 ppb, 1 ppb or
0.5 ppb; an NV.sup.- concentration equal to or less than 0.15 ppb,
0.1 ppb, 0.05 ppb, 0.001 ppb, 0.0001 ppb or 0.00005 ppb or an
NV.sup.- concentration equal to or greater than 0.1 ppm, 0.5 ppm,
1.0 ppm, 2.0 ppm, 3 ppm, 4 ppm or 5 ppm; and a total concentration
of .sup.13C equal to or less than 0.9%, 0.7%, 0.4% 0.1%, 0.01%, or
0.001%. The use of high purity quantum grade single crystal CVD
synthetic diamond material improves the decoherence time of the one
or more quantum spin defects within the diamond material and makes
it possible to isolate single defect centres using optical
techniques known to the person skilled in the art. The material may
fall into one of two categories depending on the desired end use:
low NV.sup.- concentration material or high NV.sup.- concentration
material.
[0068] In addition to controlling the concentration of point
defects within the quantum spin defect layer, it is also
advantageous to ensure that the concentration of extended
crystallographic defects such as dislocations defects is low so as
to improve optical properties of the layer (e.g. reduce
birefringence) and so as to reduce strain in the layer which can
reduce the decoherence time of the quantum spin defects.
Accordingly, birefringence in a direction perpendicular to the
quantum spin defect layer may be equal to or less than
5.times.10.sup.-5, 1.times.10.sup.-5, 5.times.10.sup.-6, or
1.times.10.sup.-6.
[0069] The layer intermediate between the electron donating layer
and the quantum spin defect layer may have a thickness equal to or
greater than: 10 nm; 50 nm; 100 nm; 500 nm; 1 .mu.m; 10 .mu.m; or
20 .mu.m. Furthermore, the intermediate layer may have a thickness
equal to or less than: 100 .mu.m; 80 .mu.m; 60 .mu.m; 40 .mu.m; or
30 .mu.m. Ranges comprising combinations of these lower and upper
boundaries for the thickness of the intermediate layer are
envisaged. The layer thickness may be optimized to ensure that
sufficient electron donation can occur between the electron
donating layer and the quantum spin defect layer to form negatively
charged quantum spin defects while ensuring that dipole coupling
between electron donating defects and quantum spin defects is low.
In an ideal scenario the intermediate layer will be very high
purity material with no defects of any kind. In such an ideal
arrangement, the electron donor layer would only contain electron
donor defects, the quantum spin defect layer would only contain
quantum spin defects, and the intermediate layer would not contain
any electron donor or quantum spin defects. This is impossible in
practice. However, the concentration of impurity defects should be
low in the intermediate layer. If the intermediate layer contains
too many defects, these may be sufficiently close to the quantum
spin defects to couple with the quantum spin defects leading to a
reduction in decoherence time. Furthermore, if the intermediate
layer contains too many defects which can accept electrons from the
electron donor layer then these defects will inhibit electron
transport from the electron donor layer to the quantum spin defect
layer. Accordingly, in certain applications the concentration of
electron donor defects such a one or more of nitrogen, phosphorous
and silicon, either alone or in combination, can be equal to or
less than: 1.times.10.sup.17 defects/cm.sup.3; 1.times.10.sup.16
defects/cm.sup.3; 5.times.10.sup.15 defects/cm.sup.3;
1.times.10.sup.15 defects/cm.sup.3; 5.times.10.sup.14
defects/cm.sup.3; 1.times.10.sup.14 defects/cm.sup.3; or
5.times.10.sup.13 defects/cm.sup.3. In many applications it is
desirable to have the concentration of these defects as low as
possible in the intermediate layer. However, in practice it is
usual that these defects will be present at a concentration of at
least 1.times.10.sup.11 defects/cm.sup.3. Furthermore, the
concentration of quantum spin defects such as NV defects can be
equal to or less than: 1.times.10.sup.14 defects/cm.sup.3;
1.times.10.sup.13 defects/cm.sup.3; 1.times.10.sup.12
defects/cm.sup.3; 1.times.10.sup.11 defects/cm.sup.3; or
1.times.10.sup.10 defects/cm.sup.3. Again, in many applications it
is desirable to have the concentration of these defects as low as
possible in the intermediate layer. However, in practice it is
usual that these defects will be present at a concentration of at
least 1.times.10.sup.9 defects/cm.sup.3.
[0070] The single crystal synthetic diamond material may have at
least one dimension equal to or greater than 0.1 mm, 0.5 mm, 1 mm,
2 mm, or 3 mm. Furthermore, the single crystal synthetic diamond
material may form a layered structure having a thickness equal to
or greater than 0.1 .mu.m, 1 .mu.m, 10 .mu.m, 100 .mu.m, 200 .mu.m,
or 500 .mu.m. The specific size and dimensions of the single
crystal synthetic diamond material will to some extent be dependent
on the device configuration and its intended use. However, for many
applications the single crystal synthetic CVD diamond material may
need to be sufficiently large to contain enough quantum spin
defects to improve sensitivity while the distribution of the
quantum spin defects is sufficiently dispersed to improve the
decoherence time of the point defects and/or make it possible to
isolate single defect centres using optical techniques.
[0071] The quantum spin defects may have a decoherence time T.sub.2
(measured by Hahn echo decay) equal to or greater than 0.05 ms, 0.1
ms, 0.3 ms, 0.6 ms, 1 ms, 5 ms, or 15 ms, with corresponding
T.sub.2* values equal to or less than 1 ms, 800 .mu.s, 600 .mu.s,
500 .mu.s, 400 .mu.s, 200 .mu.s, 150 .mu.s, 100 .mu.s, 75 .mu.s, 50
.mu.s, 20 .mu.s, or 1 .mu.s.
[0072] The quantum spin defects may be positioned at a distance
from a surface of the single crystal synthetic diamond material
equal to or less than: 100 nm; 80 nm; 50 nm; 20 nm; or 10 nm. It
can be advantageous that the point defects are positioned close to
the surface in order to increase sensitivity to changes in the
magnetic or electric field adjacent the surface.
[0073] An out-coupling structure may be formed at a surface of the
single crystal synthetic diamond material for increasing
out-coupling of light and increasing light collection from quantum
spin defects in the synthetic diamond material. In one type of
arrangement, the out-coupling structure is formed in a surface of
the single crystal synthetic diamond material whereby the
out-coupling structure is integrally formed by the surface of the
single crystal synthetic diamond material. In order to form such an
integrated out-coupling structure, more diamond material may be
required and at least a portion of this additional material can
optionally be made of a lower grade than the layered structure
comprising the quantum spin defects utilized in quantum
applications. Suitable out-coupling structures include one or more
of: a convex surface; a microlens array; a solid immersion lens
(SIL); a plurality of surface indentations or nano-structures; a
diffraction grating; a fresnel lens; and a coating such as an
antireflective coating.
[0074] A synthetic diamond device component as described above can
be manufactured using a CVD method which uses a single crystal
diamond substrate with a growth surface having a density of defects
equal to or less than 5.times.10.sup.3 defects/mm.sup.2 or
5.times.10.sup.3 defects/mm.sup.2 as revealed by a revealing plasma
etch. This may be formed of a natural, HPHT, or CVD synthetic
diamond material. Although each of these different types of diamond
material have their own distinct features and are thus identifiable
as distinct, the key feature for this substrate is that the growth
surface is carefully prepared to have a good surface finish. The
growth surface is preferably oriented within a few degrees of a
{100}, {110}, {111} or {113} crystallographic plane. The defect
density at the growth surface is most easily characterised by
optical evaluation after using a plasma or chemical etch optimised
to reveal the defects (referred to as a revealing plasma etch),
using for example a brief plasma etch of the type described
below.
[0075] Two types of defects can be revealed:
1) Those intrinsic to the substrate material quality. In selected
natural diamond the density of these defects can be as low as
50/mm.sup.2 with more typical values being 10.sup.2/mm.sup.2,
whilst in others it can be 10.sup.6/mm.sup.2 or greater. 2) Those
resulting from polishing, including dislocation structures and
microcracks forming chatter tracks along polishing lines. The
density of these can vary considerably over a sample, with typical
values ranging from about 10.sup.2/mm.sup.2, up to more than
10.sup.4/mm.sup.2 in poorly polished regions or samples.
[0076] The preferred low density of defects is such that the
density of surface etch features related to defects is below
5.times.10.sup.3/mm.sup.2, and more preferably below
10.sup.2/mm.sup.2. It should be noted that merely polishing a
surface to have low surface roughness does not necessarily meet
these criteria as a revealing plasma etch exposes defects at and
just underneath the surface. Furthermore, a revealing plasma etch
can reveal intrinsic defects such as dislocations in addition to
surface defects such as microcracks and surface features which can
be removed by simple polishing.
[0077] The defect level at and below the substrate surface on which
the CVD growth takes place may thus be minimised by careful
selection and preparation of the substrate. Included here under
"preparation" is any process applied to the material from mine
recovery (in the case of natural diamond) or synthesis (in the case
of synthetic material), as each stage can influence the defect
density within the material at the plane which will ultimately form
the substrate surface when preparation as a substrate is complete.
Particular processing steps may include conventional diamond
processes such as mechanical sawing, lapping and polishing (in this
application specifically optimised for low defect levels), and less
conventional techniques such as laser processing, reactive ion
etching, ion beam milling or ion implantation and lift-off
techniques, chemical/mechanical polishing, and both liquid chemical
processing and plasma processing techniques. In addition, the
surface R.sub.Q measured by stylus profilometer, preferably
measured over a 0.08 mm length, should be minimised, typical values
prior to any plasma etch being no more than a few nanometers, i.e.
less than 10 nanometers. R.sub.Q is the root mean square deviation
of surface profile from flat (for a Gaussian distribution of
surface heights, R.sub.Q=1.25Ra. For definitions, see for example
"Tribology: Friction and Wear of Engineering Materials", I M
Hutchings, (1992), Publ. Edward Arnold, ISBN 0-340-56184).
[0078] One specific method of minimising the surface damage of the
substrate is to include an in situ plasma etch on the surface on
which the homoepitaxial diamond growth is to occur. In principle
this etch need not be in situ, nor immediately prior to the growth
process, but the greatest benefit is achieved if it is in situ,
because it avoids any risk of further physical damage or chemical
contamination. An in situ etch is also generally most convenient
when the growth process is also plasma based. The plasma etch can
use similar conditions to the deposition or diamond growing
process, but with the absence of any carbon containing source gas
and generally at a slightly lower temperature to give better
control of the etch rate. For example, it can consist of one or
more of the following:
(i) An oxygen etch using predominantly hydrogen with optionally a
small amount of Ar and a required small amount of 0.sub.2. Typical
oxygen etch conditions are pressures of 50-450.times.10.sup.2 Pa,
an etching gas containing an oxygen content of 1 to 4 percent, an
argon content of 0 to 30 percent and the balance hydrogen, all
percentages being by volume, with a substrate temperature
600-1100.degree. C. (more typically 800.degree. C.) and a typical
duration of 3-60 minutes. (ii) A hydrogen etch which is similar to
(i) but where the oxygen is absent. (iii) Alternative methods for
the etch not solely based on argon, hydrogen and oxygen may be
used, for example, those utilising halogens, other inert gases or
nitrogen.
[0079] Typically the etch consists of an oxygen etch followed by a
hydrogen etch and then moving directly into synthesis by the
introduction of the carbon source gas. The etch time/temperature is
selected to enable remaining surface damage from processing to be
removed, and for any surface contaminants to be removed, but
without forming a highly roughened surface and without etching
extensively along extended defects such as dislocations which
intersect the surface and thus cause deep pits. As the etch is
aggressive, it is particularly important for this stage that the
chamber design and material selection for its components be such
that no material is transferred by the plasma from the chamber into
the gas phase or to the substrate surface. The hydrogen etch
following the oxygen etch is less specific to crystal defects
rounding off the angularities caused by the oxygen etch which
aggressively attacks such defects and providing a smoother, better
surface for subsequent growth.
[0080] At least a portion of the quantum diamond component can be
grown using a gas phase having a nitrogen concentration of less
than or equal to 250 parts per billion, 200 parts per billion, 150
parts per billion, or 120 parts per billion, calculated as
molecular nitrogen. The decreased nitrogen content in the gas
within the CVD reactor results in a decreased nitrogen content
within the CVD diamond material, and therefore a lower absorption
coefficient and longer decoherence times. The nitrogen content
within the CVD reactor gas may be more than 0.001 parts per
billion, more than 0.01 parts per billion, more than 0.1 parts per
billion, more than 1 part per billion, or more than 10 parts per
billion.
[0081] The CVD growth process may use source gases of high isotopic
purity in addition to high chemical purity. For example the carbon
source gas may have a .sup.12C fraction increased so as to be equal
to or greater than 99%, 99.3%, 99.6%, 99.9%, 99.99%, or 99.999%.
This can further increase the decoherence time of the single photon
emitters although it is also envisaged that a natural abundance of
.sup.12C may be used.
[0082] In light of the above, the quantum diamond component may be
formed of a diamond material having at least one high purity
portion comprising one or more of: a neutral single substitutional
nitrogen concentration equal to or less than 20 ppb, 10 ppb, 5 ppb,
1 ppb or 0.5 ppb; an NV.sup.- concentration equal to or less than
0.15 ppb, 0.1 ppb, 0.05 ppb, 0.001 ppb, 0.0001 ppb, or 0.00005 ppb;
and a total concentration of .sup.13C equal to or less than 0.9%,
0.7%, 0.4% 0.1%, 0.01%, or 0.001%.
[0083] The gas composition used in the CVD growth process might
also include other impurities related to the formation of colour
centres or their charge stabilization such as, for example, silicon
or phosphorous. However, according to certain embodiments in
addition to low nitrogen concentrations, the CVD growth process
preferably also uses a gas composition which has very low
concentrations of other impurities which may be incorporated into
the diamond material during CVD growth. Accordingly, at least a
portion of the diamond material preferably has one or more of: a
boron concentration of 100 ppb or less; a silicon concentration of
100 ppb or less; a concentration of paramagnetic defects of 1 ppm
or less; a concentration of any single non-hydrogen impurities of 5
ppm or less; a total impurity content excluding hydrogen and its
isotopes of 10 ppm or less; and a concentration of hydrogen
impurities in the single crystal diamond host material of 10.sup.18
cm.sup.-3 or less. The high purity material preferably also has a
low concentration of dislocations. For example, the high purity
single crystal diamond material may contain a dislocation bundle
density equal to or less than: 10.sup.6 dislocations cm.sup.-2;
10.sup.4 dislocations cm.sup.-2; 3.times.10.sup.3 dislocations
cm.sup.-2; 10.sup.3 dislocations cm.sup.-2; 10.sup.2 dislocations
cm.sup.-2; or 10 dislocations cm.sup.-2. This can be achieved by
careful substrate preparation and the use of nitrogen to inhibit
the formation of dislocations which could otherwise propagate
through the high purity diamond material.
[0084] It is also desirable to process a surface of the diamond
material so as to achieve a low surface roughness Rq. As described
in WO 2010010344 and WO 2010010352, high T.sub.2 values and high
spectral stability can be obtained using the synthetic diamond
material of the present invention as a host material where the
quantum spin defect is to be positioned at a distance of equal to
or less than 100 .mu.m from such a processed surface. According to
embodiments of the present invention the quantum spin defect may
optionally be positioned at a distance of equal to or less than 100
.mu.m, preferably 50 .mu.m, preferably 20 .mu.m, preferably 10
.mu.m, preferably 1 .mu.m, preferably 500 nm, preferably 200 nm,
preferably 50 nm, preferably 20 nm, or preferably 10 nm from such a
processed surface. This positioning of the quantum spin defect
means that it is readily accessible for end applications such that
it can be characterised and "read out", for example, by optical
coupling to a waveguide. Thus, it is advantageous to form a quantum
spin defect in the quantum grade single crystal diamond, wherein a
surface of the diamond material is processed such that the surface
roughness, Rq of the single crystal diamond within an area defined
by a circle of radius of about 5 .mu.m centred on the point on the
surface nearest to where the quantum spin defect is formed is equal
to or less than about 10 nm, 5 nm, 1 nm, or 0.5 nm.
[0085] In additional to low surface roughness at a surface near a
quantum spin defect, it is also useful to ensure that sub-surface
damage is low near a quantum spin defect. Sub-surface damage may be
reduced by etching, such as with a plasma etch, and polishing. It
may also be useful to control the type of surface termination at a
diamond surface near the quantum spin defect to ensure that the
diamond is not terminated with a species which will adversely
interact with the quantum spin defect. For example, it may be
useful to ensure that the diamond surface near the quantum spin
defect is terminated with a spin-zero species such as oxygen,
rather than a species which has a non-zero spin such as hydrogen or
those species which might lead to some surface charge
redistribution processes (such as that known to occur with
hydrogen).
[0086] Synthetic diamond device components as previously described
can be used to form a diamond quantum device. An example of such a
device is illustrated in FIG. 5. The quantum device 50 comprises a
diamond quantum component 52 formed of a layered single crystal
synthetic diamond material 52 as previously described. The quantum
device also comprises a light source 56 for optically pumping one
or more of the plurality of quantum spin defects in the layer
52.
[0087] The light source 56 is tuned to an appropriate frequency to
excite the NV.sup.- defect into undergoing an electron transition
as illustrated in FIG. 1(a). The electronic structure of the defect
allows the defect to be optically pumped into its electronic ground
state allowing such defects to be placed into a specific electronic
spin state even at non-cryogenic temperatures. This can negate the
requirement for expensive and bulky cryogenic cooling apparatus for
certain applications where miniaturization is desired. Further
transitions and subsequent decay and fluorescent emission will
result in the emission of a photon which all having the same spin
state. As such, this device configuration can function as a source
of photons which all having the same spin state which is useful for
further quantum processing applications based on photonics.
[0088] FIG. 6 shows a similar diamond quantum device 60. This
device 60 also comprises a diamond quantum component 62 including a
layered single crystal synthetic diamond material 64 as previously
described. The quantum device also comprises a light source 66 for
optically pumping one or more of the plurality of quantum spin
defects in the layer 64.
[0089] The diamond quantum device 60 shown in FIG. 6 differs from
that shown in FIG. 5 in that the single crystal synthetic diamond
component 62 has been formed to have an out-coupling structure 68
to increase light output from the emitting NV.sup.- defects. In the
illustrated arrangement the single crystal CVD synthetic diamond
component 60 has been formed into a solid immersion lens. This lens
may be formed entirely from a layered quantum grade material as
previously described or may be a composite structure in which the
layered quantum grade material is disposed. For example, the single
crystal synthetic diamond component 62 may be composed of a single
crystal of synthetic CVD diamond material comprising the layered
quantum grade material and one or more further layers of material
of a lower grade.
[0090] FIG. 7 shows another example of a diamond quantum device 70.
This device includes a single crystal synthetic diamond component
72 and a light source 76 as previously described. The device 70
differs from that illustrated in FIGS. 5 and 6 in that it further
comprises a detector 78 for detecting emission from one or more
decaying quantum spin defects 74 in the single crystal synthetic
diamond component 72.
[0091] In this device configuration, any perturbation of the
NV.sup.- defects which results in an electron transition to a
m.sub.s=.+-.1 state will result in a reduction in fluorescent
emission which can then be detected by the detector 78.
[0092] FIG. 8 shows another example of a diamond quantum device 80.
This device includes a single crystal synthetic diamond component
82 and a light source 86 as previously described. The device 80
also comprises a detector 88 for detecting emission from one or
more decaying quantum spin defects 84 in the single crystal
synthetic diamond component 82. The device 80 differs from that
illustrated in FIG. 7 in that it further comprises a microwave
generator 89 for manipulating one or more of the plurality of
quantum spin defects in the single crystal synthetic diamond
layer.
[0093] In this device configuration, the diamond quantum device can
function as a magnetometer, the microwave generator 89 being
configured to scan a range of microwave frequencies for
manipulating one or more of the plurality of quantum spin defects
in the single crystal synthetic diamond component 82. At a certain
frequency the NV.sup.- defects will undergo an electron transition
from the m.sub.s=0 to an m.sub.s=.+-.1 state resulting in a
decrease in the fluorescent emission from the NV.sup.- defects. The
frequency at which this transition will occur will depend on the
energy level of the m.sub.s=.+-.1 states which will be perturbed by
an external magnetic or electric field. As such, the frequency at
which a decrease in fluorescent emission occurs can be used to
measure an external magnetic or electric field.
[0094] In a modified version of the device shown in FIG. 8, the
device may also comprise a static field generator to split the
degeneracy of the m.sub.s=.+-.1 states, the magnitude of this
splitting then being perturbed by any external magnetic or electric
field leading to a change in the frequency at which a decrease in
fluorescent emission occur, this change corresponding to a change
in magnitude and/or direction of an external magnetic or electric
field.
[0095] Alternatively, the diamond quantum device illustrated in
FIG. 8 may be configured to function as a quantum information
processing device. In such an arrangement, the microwave generator
89 can be configured to selectively manipulate the plurality of
quantum spin defects in the single crystal synthetic diamond
component in order to write information to the plurality of quantum
spin defect and the detector 88 can be configured to selectively
address one or more of the plurality of quantum spin defects in
order to read information from the plurality of quantum spin
defects.
[0096] The device may be a spin resonance device, the microwave
generator being configured to scan a range of microwave frequencies
for manipulating one or more of said quantum spin defects in the
synthetic single crystal diamond material, the spin resonance
device further comprising a radio or microwave frequency generator
configured to scan a range of frequencies for manipulating quantum
spins within a sample disposed adjacent the synthetic single
crystal diamond material. FIG. 9 shows an example of such a diamond
quantum device 90. This device includes a single crystal synthetic
diamond component 92. The device 90 also comprises a detector 95
for detecting emission from one or more decaying quantum spin
defects in the single crystal CVD synthetic diamond component 92
and a microwave generator 96 for manipulating one or more of the
plurality of quantum spin defects in the single crystal synthetic
diamond component. The microwave generator 96 is configured to scan
a range of microwave frequencies for manipulating one or more of
the plurality of quantum spin defects in the single crystal
synthetic diamond layer. The device 90 further comprises a radio or
microwave frequency generator 98 configured to scan a range of
frequencies for manipulating quantum spins within a sample 99
disposed adjacent the single crystal synthetic diamond component
92.
[0097] This device configuration can function as a spin resonance
device. Such a device may also comprise a static field generator.
In such an arrangement, the sample 99 is subjected to a static
field, e.g. a static magnetic field. By applying a static magnetic
field to the sample 99, the spins of nuclei within the sample are
preferentially aligned with the applied magnetic field. An
oscillating field is then applied to the sample and the frequency
varied. When the oscillating field comes into resonance with a
nuclear spin it flips the nuclear spin to be oriented against the
direction of the static field. This transition leads to a change in
the local magnetic field which can be sensed and detected.
Different nuclei will spin-flip at different frequencies of the
applied oscillating field due to local shielding effects of
surrounding electrons and spin-spin interactions between closely
spaced nuclear spins.
[0098] So far, the described device functions like a standard NMR
device but with a much smaller sample volume and a much lower
static field allowing the use of, for example, a small magnet (or
indeed no magnet if the earth's magnetic field is used) and thus
allowing miniaturization of the device as a whole. In contrast to a
standard NMR device, changes in the local magnetic field resulting
from nuclear spin flipping are detected using one or more quantum
spin defects disposed in the single crystal CVD synthetic diamond
component 92 adjacent the sample 99.
[0099] NV.sup.- defects are disposed within the previously
described static magnetic field. Accordingly, the degeneracy of the
electron spin states m.sub.s=.+-.1 within the NV.sup.- defects is
split as illustrated in FIG. 1b. The NV.sup.- defects are excited
with an optical laser source at 532 nm causing excitation of
electrons from the .sup.3A ground state to the .sup.3E excited
state. The excited m.sub.s=0 electrons fluoresce on transition back
to the ground state emitting and this fluorescence is detected. An
oscillating microwave field is applied to the NV.sup.- defects and
the frequency varied. When the oscillating microwave field comes
into resonance with the electron spin of an NV.sup.- centres it
causes an electron to undergo a transition to m.sub.s=.+-.1 state.
The resonant spin transitions can be probed by sweeping the
microwave (MW) frequency resulting in characteristic dips in the
optically detected magnetic resonance (ODMR) spectrum as previously
described by Steinert et al. with reference to FIG. 2a.
[0100] Now, the energy of the m.sub.s=.+-.1 state will be dependent
on the static field but will be perturbed by local variations in
the magnetic field caused by the nuclear spin flipping in the
sample induced by the oscillating field. As such, the microwave
frequency at which electron spin resonance will occur in the
NV.sup.- defects will be shifted when nuclear spins in the sample
come into resonance with the oscillating field. These changes are
detected by a shift in the dip at which fluorescence occurs. As
such, nuclear spin resonance in the sample is optically detected
via changes in the electron spin resonance in the NV.sup.- defects.
The optical signal can thus be processed to generate NMR data. This
may be in the form of an NMR spectrum indicating chemical shift
data. Alternatively, or additionally, the spin resonance device may
be a spin resonance imaging device, the detector being configured
to spatially resolve emission from said quantum spin defects in the
synthetic single crystal diamond material to form a spin resonance
image. For example, a magnetic resonance image (MRI) can be
generated for a sample if a plurality of optical readings are taken
at different positions of the sample. In such a spin resonance
imaging device, the detector can be configured to spatially resolve
emission from the plurality of quantum spin defects in the single
crystal CVD synthetic diamond component to form a spin resonance
image. Alternatively, or additionally, changes in the electric
field can be measured using this technique.
[0101] Data generated using the aforementioned processed may be
displayed on a display screen of the device. Alternatively, data
may be transmitted, either wired or wirelessly, to an external
device such as a laptop or desktop computer for processing and
display. In this case, the processing and display within the
quantum device can be simplified and reduced in size and cost. A
suitable computer program can be provided to run on a standard
computer for receiving, processing and displaying data gathered by
a portable quantum device.
[0102] A quantum device as previously described may be configured
to be a microfluidic device comprising a microfluidic channel for
receiving a fluid sample, the single crystal synthetic diamond
component being located adjacent the microfluidic channel. In such
an arrangement, the microfluidic channel and the single crystal
synthetic diamond component acting as a quantum sensor can be
integrated into a microfluidic cell such as that illustrated in
FIG. 10.
[0103] FIG. 10 shows an example of a diamond based microfluidic
cell 100. The microfluidic cell 100 comprises at least one diamond
sensor 102 positioned adjacent a channel 104 into which a fluid
sample can be disposed. The at least one diamond sensor 102
comprises one or more quantum spin defects 106 which may be formed
using the layered structure as previously described. The diamond
sensor 102 is positioned adjacent the channel 104 to sense changes
in the magnetic and/or electric field within a sample located in
the channel 104. The illustrated arrangement comprises two diamond
sensing elements 102 placed on opposite sides of the channel 104.
However, it is envisaged that the microfluidic cell may comprise
only one or alternatively a plurality of diamond sensing
elements.
[0104] The microfluidic channel preferably has at least one
dimension equal to or less than 1 mm, more particularly in the
range 100 nm to 1 mm, optionally in the range 500 nm to 500 .mu.m.
The size of the microfluidic channel may be chosen to be selective
of certain species. More than one channel may be provided. The
different channels may have different sizes to be selective of
different species based on differences in the size of the
species.
[0105] FIG. 11 shows a spin resonance device 110 for use with a
microfluidic cell such as that shown in FIG. 10. The device 110
comprises a static magnetic field generator (B.sub.0), a first
variable oscillating magnetic field generator (B.sub.1) and a
second variable oscillating magnetic field generator (B.sub.2). The
first variable oscillating magnetic field generator (B.sub.1) is
preferably a radio frequency generator and the second oscillating
variable magnetic field generator (B.sub.2) is preferably a
microwave generator. The device may further comprise magnetic
shielding 112 disposed around a cell receiving bay 114. In one
arrangement the earth's magnetic field is used as a static magnetic
field and thus no additional static magnetic field generator is
required. In such an arrangement, the shielding may be adapted to
shield the sensor from any external oscillating fields but not
against a static magnetic field. Such shielding is known to those
skilled in the art. The spin resonance device also comprises a
light source 116 configured to excite quantum spin defects in a
diamond based microfluidic cell mounted in the cell receiving bay
114 and an optical detector 118 for detecting optical output
signals from the quantum spin defects in the diamond based
microfluidic cell. The light source may be a laser light source.
The light source may be configured to selectively excite quantum
spin defects at different positions along the microfluidic channel
to allow analysis of fluid at different positions along the
channel. Alternatively or additionally, the detector may be
configured to selectively detect emission from quantum spin defects
at different positions along the microfluidic channel to allow
analysis of fluid at different positions along the channel.
[0106] Alternatively to the above, the device may be a quantum
information processing device. In such devices, the microwave
generator can be configured to selectively manipulate quantum spin
defects in the synthetic single crystal diamond material in order
to write information to said quantum spin defects, the detector
being configured to selectively address one or more of the quantum
spin defects in order to read information from the quantum spin
defects.
[0107] In an alternative arrangement, the previously described
magnetic field generators may be replaced with electric field
generators. The electronic structure of the NV.sup.- defect is such
that embodiments of the present invention can also be used to
measure electric fields as an alternative to, or in addition to,
magnetic fields.
[0108] One or more processors 120 may be disposed within the spin
resonance device and linked to the detector 118 to receive and
process emission data. The one or more processors 120 may be linked
to an output 122 for outputting results. The output 122 may
comprise a display screen for displaying spin resonance data. The
one or more processors 120 and the display 122 may be integrated
into the spin resonance device. Alternatively, or additionally, the
output 122 may be adapted for transmitting data to an external
device such as a laptop or desktop computer for processing and
displaying data.
[0109] Such a device can function as previously described in
relation to FIG. 9. As an alternative, or in addition to, the use
of high purity quantum grade single crystal diamond material to
improve the decoherence time of the one or more quantum spin
defects within the diamond material, a suitable pulse sequence may
be selected and utilized to increase decoherence time. As such, the
devices previously described may be configured to impart a pulsed
signal to the one or more quantum spin defects to increase
decoherence time and thus improve sensitivity. A typical pulse
sequence would comprise a .pi./2 pulse followed by a .pi. pulse
followed by another .pi./2 pulse.
[0110] While this invention has been particularly shown and
described with reference to preferred embodiments, it will be
understood to those skilled in the art that various changes in form
and detail may be made without departing from the scope of the
invention as defined by the appendant claims.
* * * * *